Bodies from outer space have hit earth in the past, causing widespread destruction. Two examples are the asteroid or comet that struck in the Gulf of Mexico 65 million years ago, creating the massive Chicxulub crater and perhaps leading to the extinction of the dinosaurs. And the fireball that exploded over an unpopulated area of Siberia in 1908, flattening trees 10 miles (16km) in all directions, and causing a magnitude 5.0 earthquake. Computersimulaties tonen aan dat het een kleine maar dichte asteroïde die boven de grond explodeerde met de kracht van enkele honderden atoombommen. If it had hit a city, the loss of life would have been catastrophic.
Kan het opnieuw gebeuren? NASA's Wide-field Infrared Survey Explorer (WISE), an earth-orbiting telescope operated by JPL, makes the possibility of an undetected killer asteroid striking earth far less likely. The WISE observatory is designed to find, track, and analyze Potentially Hazardous Asteroids (PHAs), asteroids in low earth orbit with diameters larger than 330 ft (100m). Als ze meten 330 ft (100 m) tot 3.300 voet (1km), worden ze beschouwd als middelgrote asteroïden. WISE heeft al ligt 4.200 voorwerpen, met een geschatte 15.000 nog te worden gelokaliseerd. NASA's objective is to eventually complete a survey of all PHAs, their size, composition, trajectory, and degree of threat.
De grootste en beschouwd als het meest gevaarlijke PHAs zijn die met een diameter van meer dan 3300 ft (1 km). 911 out of an existing total of 981 (93%) of these largest asteroids have been located and analyzed. Some are the size of a small mountain, and if one were to impact our planet the consequences would be devastating. In the past, a PHA – one with a diameter of 330 ft (100m) or more — has struck earth on the average of once every one million years. Maar nu NASA heeft de mogelijkheid om in te zoomen op en verzending robot ruimtevaartuig op een asteroïde in baan om de aarde. It's possible that a vehicle could land on and apply enough rocket power to the threatening asteroid to move its trajectory away from earth.
When you consider that there have been no recorded human fatalities from meteor or asteroid strikes in modern history, but that more than 1,200,000 die every year in automobile accidents around the world, the asteroid risk factor is exceptionally low compared with driving your car.

























